Continuous self-test of a gyroscope

Abstract

A microelectromechanical gyroscope includes a drive loop having a drive element and a drive loop circuitry. The drive loop circuitry includes a clock generating circuitry for generating from the quadrature-phase detection signal a test clock signal, an angular rate phase demodulation signal and a quadrature phase demodulation signal. A sense loop includes a sense element and sense loop circuitry for detecting angular rate and producing a force-feedback signal. A test signal generator receives a quadrature-phase detection signal to be used as a quadrature-phase carrier signal and the test clock signal A summing element sums a test signal with the force-feedback signal to form a sense feedback signal. A rate phase demodulator produces a rate signal by demodulating a sense signal received from the sense loop with the angular rate phase demodulation signal, and a quadrature-phase demodulator produces a quadrature-phase output signal.

The invention claimed is: 
     
       1. A microelectromechanical (MEMS) gyroscope, comprising:
 a drive loop comprising
 a drive element configured to be excited into a vibrational primary motion in a first direction and comprising a drive detection transducer that detects motion of the drive element and generates a first electrical signal; and 
 drive loop circuitry configured to receive from the drive detection transducer associated with the drive element the first electrical signal for producing a quadrature-phase detection signal that corresponds to position of the drive element, the drive loop circuitry comprising a clock generating circuitry for generating from the quadrature-phase detection signal at least one test clock signal, an angular rate phase demodulation signal and a quadrature phase demodulation signal to be used as a quadrature-phase carrier signal, wherein a distinctive fundamental frequency of each one of at least two test frequency signals carried by the at least one test clock signal is obtained by dividing a quadrature-phase carrier signal frequency with an integer value, and wherein the test clock signal switches state at a zero crossing of the quadrature phase carrier signal; 
 
 a sense loop comprising:
 a sense element configured to be driven into a vibrational sense motion in a direction that is perpendicular to the first direction and comprising a sense detection transducer detects motion of the sense element and generates a second electrical signal, wherein the vibrational sense motion of the sense element is caused by Coriolis-force affecting a mass moving in or with the vibrational primary motion of the drive element in the first direction; and 
 sense loop circuitry configured to receive from the sense detection transducer the second electrical signal corresponding to position or speed of the sense element and to generate a force-feedback signal on basis of the second electrical signal; 
 
 a test signal generator configured to receive from the drive loop circuitry the quadrature-phase carrier signal, and the at least one test clock signal carrying the at least two test frequency signals, and to generate a test signal in quadrature phase by modulating the quadrature-phase carrier signal with the at least two test frequency signals; 
 a summing element configured to sum the test signal with the force-feedback signal to form a sense feedback signal to be fed back towards the sense element by a feedback transducer, wherein the sense feedback signal controls a force restricting the vibrational sense motion; 
 a rate phase demodulator configured to produce a rate signal by demodulating a sense signal received from the sense loop with the angular rate phase demodulation signal, wherein the rate signal comprises angular rate information; and 
 a quadrature-phase demodulator configured to produce a quadrature-phase output signal by demodulating the sense signal received from the sense loop with the quadrature-phase demodulation signal, wherein the quadrature-phase output signal comprises self-test information. 
 
     
     
       2. The MEMS gyroscope according to  claim 1 , wherein the at least one test clock signal is in quadrature phase. 
     
     
       3. The MEMS gyroscope according to  claim 1 , wherein the sense loop circuitry comprises a frontend circuitry configured to receive the second electrical signal and to produce a sense loop output signal and a backend circuitry comprising at least one of a damping circuitry for damping the force-feedback signal and an amplifier for amplifying the sense loop output signal to produce the sense signal. 
     
     
       4. The MEMS gyroscope according to  claim 1 , wherein the distinctive fundamental test frequencies are selected such that the modulated test frequency signals are within a signal band of the sense loop. 
     
     
       5. The MEMS gyroscope according to  claim 1 , further comprising:
 a quadrature correction circuitry configured to generate a quadrature feedback signal from the quadrature-phase output signal and to feed the quadrature feedback signal towards the sense element; 
 wherein frequencies of the at least two modulated test frequency signals are outside a signal band of the quadrature correction circuitry or one or more quadrature correction electrodes are configured to input the quadrature feedback signal towards the sense element. 
 
     
     
       6. The MEMS gyroscope according to  claim 1 , wherein the MEMS gyroscope comprises capacitive or piezoresistive electrodes for drive, detection and feedback of the drive element and for detection and force-feedback of the sense element. 
     
     
       7. The MEMS gyroscope according to  claim 1 , wherein the quadrature-phase detection signal is configured to be obtained at an output of a charge sensitive amplifier of the drive loop circuitry. 
     
     
       8. A method for continuous self-testing of a microelectromechanical (MEMS) gyroscope, the method comprising:
 receiving a quadrature-phase detection signal from a drive detection transducer of a drive loop circuitry of the gyroscope, wherein the quadrature-phase detection signal corresponds to position of a drive element of the gyroscope; 
 generating from the quadrature-phase detection signal, at least one test clock signal carrying at least two test frequency signals with distinctive fundamental test frequencies, a rate phase demodulation signal, and a quadrature-phase demodulation signal to be used as a quadrature-phase carrier signal, wherein the distinctive fundamental test frequencies of each one of said at least two test frequency signals carried by said at least one test clock signal is obtained by dividing a quadrature-phase carrier signal frequency with an integer value and wherein the test clock signal switches state at a zero crossing of the quadrature-phase carrier signal; 
 generating a test signal in quadrature phase by modulating the quadrature-phase carrier signal with the at least two test frequency signals; 
 receiving a second electrical signal from a sense detection transducer, the second electrical signal corresponding to position or speed of a sense element of the gyroscope, wherein a vibrational sense motion of the sense element is caused by Coriolis-force affecting a mass moving in or with the vibrational primary motion of the drive element in a first direction; 
 generating a force-feedback signal in a sense loop of the gyroscope on basis of the second electrical signal; 
 summing the test signal into the force-feedback signal to produce a sense feedback signal; 
 feeding, by a feedback transducer, the sense feedback signal towards the sense element of the gyroscope; 
 producing a rate signal by demodulating a sense signal received from the sense loop with the rate phase demodulation signal, wherein the rate signal comprises angular rate information; and 
 producing a quadrature-phase output signal by demodulating the sense signal received from the sense loop with the quadrature-phase demodulation signal, wherein the quadrature-phase output signal comprises self-test information. 
 
     
     
       9. The method according to  claim 8 , wherein the at least one test clock signal is in quadrature phase. 
     
     
       10. The method according to  claim 8 , wherein the method further comprises
 producing a sense loop output signal on basis of the second electrical signal, and at least one of:
 damping the force-feedback signal before said summing, and 
 amplifying the sense loop output signal to produce the sense signal. 
 
 
     
     
       11. The method according to  claim 8 , wherein the distinctive fundamental test frequencies are selected such that the modulated test frequency signals are within a signal band of the sense loop. 
     
     
       12. The method according to  claim 8 , further comprising:
 generating, by a quadrature correction circuitry, a quadrature feedback signal from the quadrature-phase output signal; and 
 feeding the quadrature feedback signal towards the sense element; 
 wherein frequencies of the at least two modulated test frequency signals are outside a signal band of the quadrature correction circuitry and/or one or more quadrature correction electrodes are configured to input the quadrature feedback signal towards the sense element.